Antimicrobial peptides, also known as anti-microbial peptides (AMPs), are a class of biologically active peptides with broad-spectrum antimicrobial activity, which are widely found in animals, plants, and microorganisms as a natural defense mechanism. Antimicrobial peptides have many advantages, such as low toxicity, low immunogenicity, rapid sterilization, and difficulty in developing drug resistance.

1. The APD3 database, maintained by the University of Nebraska, contains over 2,500 antimicrobial peptides;
2. The DRAMP database records 17,349 antimicrobial peptide sequences, including 4,571 common sequences, 12,704 patented antimicrobial peptide sequences and 74 antimicrobial peptides under drug discovery;
3. BaAMPs contains about 200 antimicrobial peptides with anti-biofilm activity .

And with the deeper research on antimicrobial peptides, novel antimicrobial peptides and their sequences have been continuously discovered and reported.

I. Antimicrobial peptide family

Based on tertiary deconstruction, common antimicrobial peptides can be categorized into six main groups:
1) Linear-helical peptides;
2) Cyclic peptides, which usually form β-folded structures with two or more disulfide bonds;
(3) Both α-helical and β-folded structures are stabilized by disulfide bonds;
4) Forms a hairpin or ring structure and contains disulfide bonds within the molecule;
5) Linear peptides containing repeated amino acid sequences;
6) Disordered short peptides;

II. Mechanism of action of antimicrobial peptides

Antimicrobial peptides have many different biological functions. Currently, the mechanism of action of antimicrobial peptides is divided into two main categories: membrane-damaging and non-membrane-damaging.
Membrane damage type mechanism of action includes carpet model, barrel class model, ring pore model, etc. It is generally accepted that antimicrobial peptides are adsorbed on the surface of the cell membrane through electrostatic interaction, and the physicochemical properties of the antimicrobial peptides and the constituents of the cell membrane are the main factors affecting the interaction between the two.
Compared with the membrane-damaged type, the mechanism of action of the non-membrane-damaged type has been less studied than the proud type, which mainly includes: 1) Binding to DNA and inhibiting DNA transcription/replication; 2) Inhibiting protein synthesis and folding; 3) Inhibiting the formation of the cell wall and so on.

III. Application of antimicrobial agents in cosmetics

Cationic antimicrobials have been discovered for the first time in the aspergillus since 1980 by Steiner et al. In the past decades, the unique structure and multiple mechanisms of action of antimicrobial peptides have been gradually studied and analyzed. Up to now, antimicrobial peptides have been used in medicine, disease transmission, food industry, agriculture, cosmetics and other fields. The following summarizes the main uses of antimicrobial peptides in the cosmetic industry.

1、As a preservative

The antimicrobial peptide can inhibit the growth of microorganisms in cosmetics, and it has good inhibition effect on Gram-negative and Gram-positive bacteria commonly found in cosmetics, and it has no toxicity and side effects on human body. The experimental results show that the: antimicrobial activity of the antimicrobial peptide is significantly better than that of nipagin methyl ester. Taking N2 of a company as an example, the efficacy of killing Escherichia coli and Pseudomonas aeruginosa in shampoo was 7 times and 5 times higher than that of nipagin methyl ester respectively, and the required concentration was much lower than that of nipagin methyl ester.
2、As an anti-inflammatory acne ingredient
Research shows that antimicrobial peptides have the ability to regulate sebum secretion and have a good inhibitory effect on bacteria such as Propionibacterium acnes, which is very effective in the prevention and treatment of pimples, acne, acne, etc., and is safe and non-irritating. Antimicrobial peptide has a wide range of applications and can be used with most cosmetic raw materials.
3、As an anti-dandruff ingredient
A study showed that after 28 days of continuous use of shampoo with added antimicrobial peptides, the scalp microenvironment was well improved, the number of Malassezia bacteria had a tendency to decrease, and the symptoms of redness and itching of the scalp caused by dilated capillaries were alleviated.

IV. Summary and outlook

At present, there have been more studies on the application of the discovered antimicrobial peptides in various industries, but the mechanism of action and the relationship between the mechanism of action and the structure are still unclear. Especially in the field of cosmetics, antimicrobial peptides have only been shown in toothpaste products for the record.

However, the subtlety of nature is that as the environment changes, organisms develop and evolve. Even though antimicrobial peptides have multiple mechanisms of action and multiple targets, microorganisms in the environment where antimicrobial peptides work will evolve. We believe that in the future, with the development of science and technology and biotechnology becoming more and more perfect, we will have a more accurate understanding of the mechanism of action of antimicrobial peptides, but also from a variety of organisms to obtain more highly active and safe antimicrobial peptides, antimicrobial peptide value in the cosmetic industry will be better utilized.

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